Roof Of Low-rise Building Research Articles

An extreme value estimation method of wind pressures based on change point theory

Estimating the extreme wind pressure accurately on the roofs of low-rise buildings is crucial for wind-resistant design in wind engineering. This study proposes a new method for extreme value estimation, where change-point theory is incorporated into selecting thresholds to determine the optimal threshold and the wind pressure coefficient is converted into an intermediate exponential variable. The measured wind pressure data collected from the roof of a low-rise building at the Pudong experimental base of Tongji University during Typhoon Ampil is used as the sample of the extreme value estimation. Referring to the position of change point, the interpolation method assists in finding the most appropriate threshold for the wind pressure coefficient. The number of independent peaks in a standard wind pressure sample is reduced from 204 to 30, applying the optimal threshold while considering the correlation. This processing is crucial to reducing the estimation error. Then, the error rates of the proposed method are below 5 % at quantile p = 0.95 and the mean error rate of the proposed extreme value estimation method is within (−0.1, 0) for the whole roof regions. For comparison, the upper limit of the mean error rate for the modified Hermite model based on zero-crossing theory reaches 0.41 and that of Quan's method based on classical extreme value theory is 0.28. These results demonstrate the superiority of the proposed method. Meanwhile, the relevant estimation results show that the proposed method's extreme wind pressure values meet engineering requirements at the specified percentile.

Wind induced peak pressures on low-rise building roofs via dynamic terrain computational methodology

Computational Wind Engineering is expanding rapidly in the last decade and is expected to be introduced as a design tool for wind-induced loads in future code provisions and standards worldwide. The paper discusses the current CWE shortcomings of the state-of-the-art and proposes a methodology that targets to close the current research gaps, from a practical point of view. Monitoring wind tunnel experiments, significant deviations of instantaneous velocity profiles due to high turbulence intensity are expected to be critical for design pressures. This inspired the novel modeling technique - named Dynamic Terrain - that reformulates the turbulence characteristics and assumes that each instantaneous profile is produced by changing the corresponding terrain conditions. Successively derived profiles from the wind tunnel are introduced as inlet conditions in coarse LES computational domain and propagate inside the domain to interact with the building. The incident flow is successfully modelled, in terms of mean, turbulence intensity and spectral content. Mean, standard deviations and peak pressure coefficients correlate well with experimental results and the procedure is advantageous compared to similar computational techniques. The target accuracy is achieved, benefits and limitations of the method are discussed, and conclusions based on experimental and computational observations are drawn.

Effect of spacing on wind-induced interference on the roof of low-rise buildings with cylindrical roof using CFD simulation

Effect of spacing on wind-induced interference on the roof of low-rise buildings with cylindrical roof using CFD simulation

Wind loading of rooftop PV panels cover plate: A codification-oriented study

The design of rooftop solar panels for wind loads requires provisions to be sufficiently comprehensive to reflect the wind effects on PV module/panel cover plate, individual PV panels, PV panels arrays, and their supporting systems. Unfortunately, the focus of the literature studies and the provisions of the current wind codes and standards is on the net pressure coefficients that can be used in the design of PV panel supporting systems. Particularly, current wind codes and standards of practice do not provide design pressure coefficients for elements on cover plates of rooftop PV panels. In this contribution and along with the intention to examine the characteristics of the wind-induced surface pressures, this paper investigates the surface wind loads of a rooftop solar array of eight panels. The tests were carried out in open-terrain exposure at a geometric test scale of 1:50. In preliminary experiments, additional tests were conducted on two more geometric scales, namely 1:100 and 1:200, to assess the effects of the geometric test scale on the experimental pressure coefficients that would be deemed as design loading for the credibility and integrity of the wind tunnel setup established for codification-oriented studies. The experimental results illustrate that applying the design net pressure coefficients of the current wind codes and standards for the design of PV cover plates will lead to significantly undervalued wind loads. On the other hand, it is found that the external pressure coefficients assigned by ASCE/SEI for gable roofs of low-rise buildings with a slope between 7° and 20° are adaptable for the design of elements on cover plates of rooftop PV panels.

The Action of Tornadoes on the Structural Elements of a Wooden Low-Rise Building Roof and Surrounding Objects—Review and Case Study

This article presents the phenomena of tornado models with statistical data on the number of tornadoes in various regions of the world. Classifications are presented of the intensity of weather phenomena caused by gusts of wind in terms of the amount of damage to buildings and nearby objects. The main aim of the article is to analyze a damaged single-family house and its surroundings after the tornado in Fairburn (2018, Georgia, USA), to estimate the peak wind speed that caused the damage, based on the ultimate and serviceable limit states, and to compare the obtained results with the tornado scales. The article draws attention to the various possibilities of damage and analyzes several places where potential damage could begin. The low-trength capacity of the joints was the direct cause of the roof structure failure, and this case is analyzed and discussed. FinallyFinally, the calculations performed are summarized and conclusions resulting from the visible trends are proposed. The novelty of this article lies in the following: the validation of the numerical model describing the response of the roof structure to the tornado; the estimation of the wind speed based on the degree of damage to the building based on the EF scale; and the analysis of the ultimate and serviceable limit states of the rafter to the horizontal beam joint.

Wind Load Analysis on Gable Roof of Low-Rise Building

The effect of pressure because of the winds on the exterior of gable roof of a low-rise single-storey building has been analyzed in present research using CFD simulation. Roof slope, which is most important factor for safety of structure was taken into consideration. Many past researchers have studied roofed structures but the majority of these researches have been carried on flat roofs, hip roof, spherical roofs, pyramidal roofs. There is need of researches that analyses effect of winds on gable roofs as these kinds of roofs are generally more susceptible to wind damage. ANSYS ICM is used for modeling and meshing and ANSYS Fluent for simulation. Results are extracted here using CFD post. In this very study three models with slope ang 10°, 20° and 30° with same incidence angle 0° were examined. This study analyses the effect of slope of the roof and angle of incidence of wind. The streamlines of velocity around the building model and pressure coefficient (Cp ) contours on the surfaces of the roof are opted here to represent the results. When results were plotted it was found that pressure coefficients were switching from negative to positive as the slope of the roof increases and the formation of vortex on leeward gets complicated as we go on increasing the slopes.

Wind Loads in Low-Rise Buildings with Parapet: A Systematic Review

A relevant analysis for the design of buildings is wind-induced loading. Although this has led to numerous studies, there have been relatively few investigations on the effects of parapets on wind loads. This systematic review addressed quantitative and qualitative behavior of wind loads in buildings with parapets in the Web of Science, ScienceDirect, SCOPUS, and Compendex databases. Using alternative methods such as citation searches and websites were selected 6 research articles were and added 6 papers. The results treat the influence of parapets on the behavior of the wind on roofs of low-rise buildings, especially wind loads, and its correlation with the building's geometric characteristics and parapets. The results identified pressure increases on roofs for low parapets (h<1.0 m); however, the dates vary according to the h/H ratio. Also, in general, the higher the parapets, the highest the reduction in the intensities of the pressure coefficients. Still, the porous and cantilevered parapets are more efficient and economically viable as a device to mitigate wind loads when compared to solid parapets in low buildings. Finally, for an open canopy, the height of the parapet is the main parameter, although the length of the building is also relevant.

Neighborhood, Topography, and Wind Direction Effects on Wind Pressure Distribution on the Low-rise Building Roof

Low-rise buildings are the majority of the houses that are constructed all over the world. Experiments of the wind loads acting on these buildings provide vital information to design secure structures and adverse weather conditions resistants, considering the basic parameters as roof slopes and the wind direction. This study estimated the distribution of wind pressures around the contour of buildings with gable roofs, considering diverse neighborhood conditions, namely the number and geometric configuration of buildings on the ground, in conjunction with the different angles of wind incidence and topography. The simulations took place with Ansys Workbench software, and the RNG K-Epsilon turbulence model and tetrahedral mesh were employed. The application validation of the CFD technique occurred in the double-sloped pitched roof structure. The results showed good concordance with the literature. The pressure coefficients were analyzed, as well, in the flow visualization, highlighting the attachment points and the recirculation zones.

Investigation of the Pressure Coefficients Correlation Field for Low-Rise Building Roofs

The use of hyperbolic paraboloid roofing (HPRs) is increasingly common in contemporary architecture, especially for buildings with large spans, making use of tensile structures or light shells. These structures are very sensitive to wind loads because of their light weight. In particular, they tend to oscillate under wind action, generating complex pressure distributions and cable instability. Therefore, for this shape structure, the investigation of wind-pressure coefficients correlations plays a relevant role in the design of structural elements. Therefore, based on wind tunnel tests, this paper investigates the behavior of four rectangular low-rise building models with HPR when immersed in a turbulent boundary layer flow. The test results were synthesized in correlation maps of the pressure coefficients. The results were evaluated as functions of different model heights and curvatures, and considering three different angles of wind incidence (0°, 45°, and 90°).

LES Analysis of the Effect of Snowdrift on Wind Pressure on a Low-Rise Building

This paper presents a comparative study of the distribution of wind pressure acting on a low-rise building roof with or without snowdrift through the Large-Eddy simulation (LES) method. Firstly, based on previous wind-blowing snow experiments, the stable snowdrift models were obtained by reverse technique. Secondly, the methodology of LES numerical simulation was introduced, where sensitivity analyses were conducted to determine a more reasonable grid configuration and data sampling time. Meanwhile, the numerical validation was also verified by comparing it with the previous PIV database. Finally, the wind pressure acting on the building’s roof with or without snowdrift were systematically compared and analyzed. It was found that the snow cover significantly restrains the size of the separation bubble and makes is lcoated earlier on the roof, which leads to the increasing passing velocity in the region near the roof. Meanwhile, the area-averaged pressure coefficient in the windward region (x/H < 0.5) for the snowdrift roof will be significantly amplified, especially for the fluctuating pressure, the maximum value of the Relative Difference even reaches 40%. Additionally, according to the POD analysis, the snowdrift causes the fluctuating wind energy to concentrate near the windward side of the roof. Therefore, more attention should be paid to the wind pressure in the windward region when the snowdrift is formed on the roof.

Life-Cycle Typhoon Risk Analysis for Roofs of Low-Rise Buildings Based on the Extremum Probability Density Evolution Method

Life-Cycle Typhoon Risk Analysis for Roofs of Low-Rise Buildings Based on the Extremum Probability Density Evolution Method

Nonstationary near-ground wind characteristics and wind-induced pressures on the roof of a low-rise building during a typhoon

Wind fields in the surface layer during typhoons usually have strong nonstationary features, which cause damage to low-rise buildings, especially their roofs. It is thus required to establish accurate models of typhoon-generated near-surface wind fields and assess typhoon effects on low-rise buildings. In this paper, a framework of extracting time-varying mean component and determining time-varying fluctuating component of nonstationary signals is established, which is applied to investigate the on-site measured near-ground nonstationary wind velocities and wind-induced pressures on the roof of a typical low-rise building during a typhoon. It is observed that near-ground wind characteristic parameters (including turbulence intensities, gust factors, peak factors and turbulence integral length scales, wind spectra) and wind pressure coefficients on the roof obtained by the nonstationary analytical approach are more reasonable than those determined by the conventional stationary analytical approach. Besides, the evolutionary power spectral density is used to examine time-frequency spectra of wind velocities and wind pressures. This comparative study based on the nonstationary and stationary analysis approaches aims to further the understanding of the nonstationary surface layer wind characteristics and wind pressures on typical low-rise buildings for reduction of windstorm damages to residential buildings in typhoon-prone regions.

Trends in modern construction

The article highlights the results of analysis and systematization of certain trends in the development of modern construction in Europe and Ukraine. It is indicated on the main directions of increasing the efficiency of investments in construction due to the improvement of structural and organizational and technological solutions.
 It was established that one of the priority areas in construction is construction processes aimed at improving the thermal protective properties of buildings, namely, the device for heat insulation of external enclosing structures of walls, roofs, windows, and external doors. This area is key in domestic and European construction. According to statistics, more than 75% of existing civil buildings in Europe and more than 90% in Ukraine do not meet modern standards for energy conservation.
 The next direction of development of construction technologies indicates the introduction of prefabricated and prefabricated monolithic structures. The direction in construction, which was recently dominant in our country and over time partially neglected, is reviving again at a rapid pace, both in Europe and in Ukraine. Full-assembly and prefabricated monolithic structures and technologies make it possible to carry out relatively simple technological processes of erecting buildings on a construction site with structures of high factory readiness. This reduces the labor intensity of construction processes, improves the quality of work and does not require a high level of qualification of individual construction professions, such as an installer.
 One of the important areas of modern construction is the reconstruction of existing buildings and territories. The reconstruction of civilian buildings is aimed at restoring the operational properties of existing buildings with a possible superstructure, extension, reconstruction and their mandatory thermal modernization. These processes include disassembly of the roofs of low-rise buildings with their subsequent superstructure, extension of balconies, improvement of adjacent areas. These activities are aimed at extending the time frame and improving the conditions for the further operation of buildings. Also, the scope of work on the reconstruction of industrial buildings and territories for objects for civil, socio-cultural purposes, that is, their revitalization, is constantly expanding.

Interference Effects of Adjacent High-Rise Building on Wind-Induced Response of Low-Rise Flat Roof Building

Interference influence of the spacing and height ratio on the modal generalized force and wind-induced response of the low-rise building roof due to one adjacent high-rise building is investigated at three typical wind directions of 0∘, 90∘ and 180∘, where the low-rise building was, respectively, located at the upstream, side-by-side and downstream of the high-rise building. The mean and standard deviation of the modal generalized force of the first vibration mode mainly exhibits reduction effects and amplification effects, respectively, at the wind direction of 0∘ and 90∘ at small building spacing, and first experiences shielding effects and then becomes amplification effects when the height ratio increases at the wind direction of 180∘. The maximum displacement mainly presents reduction effects at the wind direction of 0∘, the interference factor decreases with the increase of the reduced frequency in engineering range, and the minimum interference factor is close to 0.2. At the wind direction of 90∘, the maximum displacement mainly presents amplification effects, these effects are obvious when the spacing ratio is small and the height ratio is large, and the maximum interference factor is close to 2.2 when the reduced frequency is larger than 0.3. At the wind direction of 180∘, the maximum displacement shows significant amplification effects when the building spacing is small and the height ratio is large, the amplification effects gradually weaken and change into shielding effects as the building spacing increases or the height ratio decreases, and the minimum interference factor is close to 0.3. The minimum displacement experiences amplification effects at all three typical wind directions.

Wind loads on multi-span roof buildings

This paper examines wind loads acting on multi-span roofs of low-rise buildings by performing wind tunnel tests with models whose parameters are roof shape (sawtooth, gable), roof slope (5°, 10°, 20°, 30°, 45°) and the number of spans (1–5). Large suctions can occur at either a high corner/edge or a low corner of sawtooth roofs, depending on roof slope and the location of roof span. Low corners of multi-span gable roofs experience large negative pressures on edge roofs of low-pitch roof slopes and on middle roofs of steeper roof slopes. Relatively large positive pressures on both sawtooth and multi-span gable roofs can occur at roof troughs of low-pitch roof slopes and their magnitude becomes larger as roof slope increases. For steeper roof slopes, large positive pressures are also observed at roof ridges of both roof shapes although their magnitude and the location of the roof span depend on roof shape. Both the size and the magnitude of suctions on walls between spans of sawtooth roofs increase with roof slope. Comparisons with ASCE7-16 design values were performed and the results imply that ASCE7-16 underestimates both positive and negative wind loads on most roof zones of multi-span roofs.

Wind Interference Effects from One High-Rise Building and Similar Low-Rise Flat-Roof Buildings

Wind tunnel tests in an open terrain were carried out to study interference effects on peak pressure coefficients of one low-rise flat-roof building due to one high-rise building and similar low-rise buildings. The results demonstrate that amplification interference effects are significant on the minimum pressures at the edge of the low-rise building roof adjacent to the high-rise building and on the maximum pressures in the roof area away from the high-rise building, where the minimum pressure means the algebraic minimum with negative suction. Magnitudes of the envelope peak pressure coefficients on the low-rise building increase when the high-rise building height increases. The envelope minimum peak pressure coefficients in the roof middle area parallel to the high-rise building experience amplification effects at large building height and small spacing ratios, but other roof areas experience shielding effects at small spacing ratios, and interference factors of the envelope minimum peak pressure coefficients increase with the increase of the height and spacing ratios. When the spacing ratio is less than two, cases with large height ratios display amplification effects on the envelope maximum peak pressure coefficients, and amplification effects increase with the increase of the height ratio or the decrease of spacing ratio.

Experimental and theoretical study on the internal pressure induced by the transient local failure of low-rise building roofs

A case study on the internal pressure induced by a local failure on the vulnerable gable roof of a low-rise building was extensively conducted experimentally and numerically. Five roof opening configurations were tested in the wind tunnel under three different boundary layer conditions, based on 1:40 scaled models. The effects of opening shape, opening position, opening ratio, building internal volume, and wind speed on peak transient and steady-state internal pressures were studied. The study results indicate that the peak transient and steady-state internal pressures and the corresponding transient overshoot ratio all increase with an increasing opening ratio. The peak steady-state internal pressure is little affected by the approaching wind speed; while the peak transient internal pressure coefficient shows a significant linear relationship with the wind speed. The coupling effect of vortex shedding and Helmholtz resonance in double building volume compensation situation may cause larger fluctuating internal pressure. Both the vortex shedding and Helmholtz resonance reduce the internal pressure coherence to some extent. The agreement between the numerical and experimental results is much better for the mean internal pressure than that for fluctuating internal pressure or peak internal pressure.

Hygienic strategy of mobile communication base station antennas radiofrequency electromagnetic field values modern control

Introduction. The urgency of the issue is due to the rapid development of new telecommunications and information technologies, the widespread introduction and distribution of cellular base stations (BS), which changes the conditions of contact of the population with sources of electromagnetic radiation of radio frequencies (EMR RF). The aim of the study is to summarize the results of the analysis of the project documentation for the placement of mobile radiotelephone network BS in terms of comparability of calculated and actually measured levels of electromagnetic radiation (EMR) from transmitting antennas; to determine the prospective tasks of hygienic control of the safety of the BS. Materials and methods. For hygienic control of EMR levels, serial broadband meters PZ-42 and NBM-550 were used; the method according to MUC 4.3.1677-03 "Determination of the levels of the electromagnetic field created by radiating technical means of television, FM radio broadcasting and base stations of land mobile radio communications". 74 BS were examined, whose antennas were a source of EMR at the frequency of 2620-2640 MHz with a power of 24.2-24.4 W. Results. The maximum length of the building restriction zone (BRZ) from the BS antennas ranged from 16 m to 101 m, regardless of the power of the radiating means, in 50% of cases the length of the BRZ was 30-45 m. In 40% of cases, BS antennas are installed on the roofs of low-rise buildings with BRZ at a height that falls to 5-10 meters from ground level. The excess of the calculated EMR values in terms of energy flux density (EFD) was determined for 50% of the BS. Instrumental measurements of EFD in 19.4% of cases showed excess remote, 11.1% - exceeding marked only by considering the expanded uncertainty (EU) measurement EFD. It was found that the values of EFD measured with EU are more closely approximated to the calculated values. Conclusions. Substantiated recommendations on whether the calculation of the era for height and length for the lower lobes in a radiation direction of antenna, recording ratio EU of the measured values of EFD for additional health human in multivariate emitters of EMR RF. The prospective tasks of hygienic control of the safety of the BS operation are defined.

Corrigendum: Effects of Freestream Turbulence on the Pressure Acting on a Low-Rise Building Roof in the Separated Flow Region

Corrigendum: Effects of Freestream Turbulence on the Pressure Acting on a Low-Rise Building Roof in the Separated Flow Region

Steady-state and transient wind characteristics of low-rise building roofs with openings in vulnerable areas

A strong wind would cause roof openings on a low-rise building and bring further structural damage. Previous related studies focused on different shapes of openings on flat roofs. Little study has been done on the sloped roofs with openings in vulnerable roof areas. In this study, wind tunnel tests were carried out to investigate the steady-state and transient internal pressure characteristics due to opening at the vulnerable roof areas of a low-rise building. The tests considered both steady-state and transient openings of roof. The experimental results indicated that the steady-state internal pressure distribution tends to be uniform and that the internal pressure induced by leeward roof ridge opening is obviously lower than that induced by the windward one. The fluctuation effect around the orifice area is apparent with the skewed wind direction and the combined effect of internal and external pressures on the unopened roof side is significantly smaller than that on the opened side. Current design provision of China for internal pressure evaluation is found to be unconservative. The transient overshoot is closely related to the opening location in the vulnerable roof area and is more pronounced when the opening is on the leeward side. Among the internal pressure coefficients commonly adopted in design, the extreme net wind pressure coefficient is most important, which is affected most at the orifice near eaves, roof corners and tails, and leeward roof ridge.